Isabella I, queen of Jerusalem (1190/92–1205), carried the shattered kingdom's legitimacy through four political marriages — the crown of Acre passing with her hand from Conrad to Henry of Champagne to Amalric of Lusignan.
Isabella was the succession: when Sibylla died at Acre in 1190, every faction's road to the crown ran through Amalric I's younger daughter, and her marriages became the kingdom's constitutional history. Forced from her beloved first husband Humphrey of Toron by the barons (1190) to legitimise Conrad of Montferrat; widowed by the Assassins' knives days after Conrad's election (1192); remarried within the week to Henry of Champagne for the same reasons of state; widowed again by a window's collapse (1197); and married last to Amalric of Lusignan, king of Cyprus.
Through it all she was the reigning queen of a kingdom rebuilt at Acre by Richard's crusade — its Jerusalem lost, its politics a regency of husbands — and she transmitted the crown intact: through her daughters ran every later claim, from Brienne and Hohenstaufen to the kings of Cyprus.
Born in 1172 to Amalric I and his Byzantine queen Maria Komnene, Isabella was raised at her mother's dower-town of Nablus, half-royal and half-Greek, at careful distance from the Courtenay faction around her half-siblings. At eight she was betrothed, at eleven married, to Humphrey IV of Toron — the wedding at Kerak celebrated, in one of the age's indelible scenes, while Saladin's siege engines battered the walls and the bridegroom's mother sent dishes from the feast out to the sultan.
The succession crisis of 1186 first made her a piece on the board: the baronial opposition at Nablus proposed crowning Isabella and Humphrey against Sibylla and Guy — and Humphrey, horrified, slipped away to do homage to Guy, postponing her queenship by four years.
The chroniclers agree on the beauty — the Lyon Eracles calls her one of the loveliest women of her time — and record, mostly in passing, the pliancy her situation enforced: eighteen years old, in love with Humphrey, she resisted the 1190 annulment until, the sources say, her formidable mother persuaded her where the barons' lawyers could not, and thereafter she performed each dynastic remarriage within days of each widowhood. What she thought is nowhere recorded; queens who are successions incarnate rarely get to say.
Flashes survive nonetheless: at Conrad's murder she barricaded herself in the Tyre citadel and — by the Muslim chronicler Ibn al-Athir's account — refused to yield the keys to anyone but Richard or her own next lawful husband: the succession, in her own person, holding a walled city. Her partnership with Henry of Champagne is the one the sources let warm slightly; five years, three daughters, and a court at Acre that briefly remembered gaiety.
Her queenship ran through proxies by law and war by circumstance: Conrad, king-elect for eight days, never crowned, murdered in a Tyre street by two Assassins (April 1192); Henry of Champagne, ruling as "lord of the kingdom" without coronation, managing the German crusade's gains (Beirut recovered) until the balcony at Acre gave way beneath him (September 1197); Amalric of Lusignan, crowned with her at Acre in January 1198, bringing Cyprus and its resources into the royal orbit and sealing the six-year truce of 1198 that let the rump kingdom breathe.
The kingdom she presided over was the Third Crusade's creation: the coastal strip from Jaffa to Beirut, capital at Acre, Jerusalem itself Saladin's — a state of ports, truces, and Italian merchant quarters whose politics her marriages held together. She died at Acre early in 1205, within weeks of Amalric; the crown passed, clean and uncontested, to her thirteen-year-old daughter Maria of Montferrat.
Isabella's biological legacy was the entire later succession: Maria of Montferrat carried the crown to John of Brienne and thence to Frederick II's house; Alice of Champagne married into Cyprus and regented Jerusalem; Melisende of Lusignan's line ran to the princes of Antioch. Every claimant to the title "king of Jerusalem" for the next six centuries — to the House of Savoy and beyond — descends from or through her.
Historians have read her reign as the demonstration case of Outremer's constitutional paradox: a kingdom whose high court could unmake marriages and make kings, but only through the body of one woman. The queen who was never not queen — through four husbands, two murders-by-fate, and the loss of the holy city itself — kept the legal thread of the First Crusade's kingdom unbroken; it was not nothing, and it was hers.